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Date: Thu, 29 Jul 2004 15:41:03 -0400 (EDT)
From: Robert Watson <rwatson@freebsd.org>
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To: Scott Long <scottl@freebsd.org>
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cc: Alan Cox <alc@freebsd.org>
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Subject: Re: cvs commit: src/sys/alpha/alpha pmap.c src/sys/amd64/amd64
	pmap.c         src/sys/i386/i386 pmap.c src/sys/vm vm_page.c
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On Thu, 29 Jul 2004, Scott Long wrote:

> >    - Enable recursion on the page queues lock.  This allows calls to
> >      vm_page_alloc(VM_ALLOC_NORMAL) and UMA's obj_alloc() with the page
> >      queues lock held.  Such calls are made to allocate page table pages
> >      and pv entries.
> 
> My understanding is that recursive mutexes are quite expensive.  Is
> recursion a common occurrance now, and is there a good way to
> profile/measure these paths? 

No opinion on the change itself, but just to clarify this wording a little
for those reading who don't follow the locking work blow-by-blow: flagging
a mutex as recursive itself is not expensive, but the act of recursing the
mutex is expensive. 

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Principal Research Scientist, McAfee Research